U.S. patent application number 17/634327 was filed with the patent office on 2022-09-29 for motor protection device.
This patent application is currently assigned to BELIMO HOLDING AG. The applicant listed for this patent is BELIMO HOLDING AG. Invention is credited to Maurizio GAETA, Thomas GAY, Stephan HAAG.
Application Number | 20220311238 17/634327 |
Document ID | / |
Family ID | 1000006418902 |
Filed Date | 2022-09-29 |
United States Patent
Application |
20220311238 |
Kind Code |
A1 |
GAETA; Maurizio ; et
al. |
September 29, 2022 |
MOTOR PROTECTION DEVICE
Abstract
Disclosed is a motor protection device (1). The motor protection
device (1) includes an interrupter unit (11, Q1, Q2) for
electrically connecting a power supply (Vcc) and an electric motor
(M) in an operation mode and electrically disconnecting the power
supply (Vcc) and the electric motor in an alternative overload
mode. The motor protection device further includes an overload
detection unit (12). The overload detection unit (12) is configured
to monitor a motor current and to control the interrupter unit (11,
Q1, Q2) to switch from the operation mode into the overload mode if
the motor current indicates an overload condition of the electric
motor (M) in the operation mode. The motor protection device (1)
further includes a recovery detection unit (13). The recovery
detection unit (13) is configured to monitor a motor temperature
and to control the interrupter unit (11, Q1, Q2) to switch from the
overload mode back into the operation mode if the motor temperature
indicates a recovery from the overload condition.
Inventors: |
GAETA; Maurizio; (Wetzikon,
CH) ; GAY; Thomas; (Flasch, CH) ; HAAG;
Stephan; (Berikon, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BELIMO HOLDING AG |
Hinwil |
|
CH |
|
|
Assignee: |
BELIMO HOLDING AG
Hinwil
CH
|
Family ID: |
1000006418902 |
Appl. No.: |
17/634327 |
Filed: |
October 2, 2020 |
PCT Filed: |
October 2, 2020 |
PCT NO: |
PCT/EP2020/077620 |
371 Date: |
February 10, 2022 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02H 7/0852
20130101 |
International
Class: |
H02H 7/085 20060101
H02H007/085 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 7, 2019 |
CH |
01271/19 |
Claims
1. A motor protection device (1), the motor protection device (1)
including: a) an interrupter unit (11, Q1, Q2) for electrically
connecting a power supply (Vcc) and an electric motor (M) in an
operation mode and electrically dis-connecting the power supply
(Vcc) and the electric motor in an alternative overload mode; b) an
overload detection unit (12), wherein the overload detection unit
(12) is configured to monitor a motor current and to control the
interrupter unit (11, Q1, Q2) to switch from the operation mode
into the overload mode if the motor current indicates an overload
condition of the electric motor (M) in the operation mode; c) a
recovery detection unit (13), the recovery detection unit (13)
being config-ured to monitor a motor temperature and to control the
interrupter unit (11, Q1, Q2) to switch from the overload mode back
into the operation mode if the motor temperature indicates a
recovery from the overload condition.
2. The motor protection device (1) according to claim 1, wherein
the motor tempera-ture is a temperature of one or more motor coils
of the electric motor (M).
3. The motor protection device (1) according to claim 2, wherein
the recovery detec-tion unit (13) is configured to monitor a
resistance of the one or more motor coil(s).
4. The motor protection device (1) according to claim 1, wherein
the motor protection device (1) is configured to electrically
connect a sensing input of the recovery detection unit with the
electric motor (M) in the overload mode and to disconnect the
sensing input and the electric motor (M) in the operation mode.
5. The motor protection device (1) according to claim 1, wherein
the motor protection device (1) includes a shunt resistor (Rshunt)
and wherein the overload detection unit (12) is configured to
monitor the motor current by measuring a voltage drop over the
shunt resistor (Rshunt).
6. The motor protection device (1) according to claim 1, wherein
mon-itoring the motor current includes comparing the motor current
with a given motor current threshold.
7. The motor protection device (1) according to claim 6, wherein
the motor current indicates an overload condition if the motor
current exceeds the motor current threshold for a given overload
time threshold.
8. The motor protection device (1) according to claim 1, wherein
mon-itoring the motor temperature includes comparing the motor
temperature with a given motor temperature threshold.
9. The motor protection device (1) according to claim 8, wherein
the motor tempera-ture indicates a recovery from the overload
condition if the motor temperature remains below the motor
temperature threshold for a given recovery time threshold.
10. The motor protection device (1) according to claim 1, wherein
at least one of the interrupter unit (11, Q1, Q2), the overload
detection unit (12) and the recovery detection unit (13) is
designed in an at least partly redundant manner.
11. An electric drive (99), wherein the electric drive (99)
includes a motor protection device (1) according to claim 1 and an
electric motor (M).
12. The electric drive (99) according to claim 11, wherein the
electric motor (M) is an electronically commutated motor.
13. The electric drive according to claim 11, wherein the electric
drive includes a power module (2), wherein the power module (2) is
electrically con-nected with the electric motor (M), and wherein
the interrupter unit (11, Q1, Q2) is electrically connected or
integral with the power module (2).
14. A method for operating an electric motor (M), the method
including the steps of: a) connecting the electric motor (M) a
power supply (Vcc) in an operation mode; b) monitoring, in the
operation mode, a motor current and switching from the operation
mode into an alternative overload mode if the motor current
indi-cates an overload condition of the electric motor (M), wherein
the electric motor (M) and the power supply are disconnected in the
overload mode; c) monitoring, in the overload mode, a motor
temperature of the electric mo-tor (M) and switching from the
overload mode back into the operation mode if the motor temperature
indicates a recovery from the overload con-dition.
15. A method for operating an electric motor (M) comprising using a
motor protection device according to claim 1.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to protection devices for
electric motors, electric drives with an electric motor and a
protection device, as well as to methods for operating an electric
motor. The invention is particularly useful in critical application
where any damage of an electric drive and/or equipment that is
actuated by an electric drive must be prevented with a high degree
of safety.
BACKGROUND OF THE INVENTION
[0002] Electric motors and drives are used in a wide variety of
applications, including safety-critical applications. Examples are
critical safety valves operated by a servo drive, or safety drives
e. g. in form of spring return drives that are used to move fire
dampers or smoke dampers as used in fire protection systems.
[0003] A general issue of concern for electric drives is the
occurrence of overload conditions that may, if not detected and
handled appropriately, at least significantly reduce the lifetime
of the motor or further components, and further cause defects
and/or severe hazards, e. g. fires due to overheating. Therefore,
appropriate detection and handling of overload conditions is at
least highly desirable and in some applications also regulatory
required.
SUMMARY OF THE INVENTION
[0004] For detecting overload conditions of an electric motor or
drive, respectively, a number of strategies and approaches is known
in the art.
[0005] In particular, it is known how to detect an overload by way
of measuring a motor temperature with temperature sensors that are,
e. g. located in the area of the motor coil(s). This approach,
however, has the disadvantage that an overload condition may be
reflected by the temperature only in delayed and slow manner.
Further, it necessarily requires temperature sensors as additional
components and additional wiring for the connection. At least the
first-mentioned drawback is also present if the motor temperature
is measured indirectly via the coil resistance.
[0006] Furthermore, it is known to detect an overload temperature
via the current that is drawn by the motor by evaluating either the
voltage drop over a shunt resistor. This approach, however, has the
general disadvantage that the current provides a criterion for
switching off the motor in case of an overload conditions, but does
not provide an optimized criterion for a recovery of the motor from
the overload condition, i. e. when the motor may again be safely
energized. Typically, the motor is powered again after a
pre-determined recovery time. Such recovery time, however, may be
too short under certain conditions and/or be unnecessarily long
under other conditions.
[0007] It is further known to detect a blocked motor by evaluating
the back-EMF (electro-motive force) that is generated by an
electric motor when running. This approach, however, is only suited
for detecting a blocked drive, but not for reliably detecting an
overload when the motor is still running.
[0008] It is an overall objective of the present invention improve
the state of the art regarding the overload protection of electric
motors and favorably to avoid at least some drawbacks of the prior
art fully or partly.
[0009] In an aspect, the overall objective is achieved by a motor
protection device. The motor protection device includes an
interrupter unit for electrically connecting a power supply and an
electric motor in a operation mode and electrically disconnecting
the power supply and the electric motor in an overload mode. In the
operation mode, the electric motor is connected with the power
supply, the motor is energized. In the overload mode the electric
motor and the power supply are disconnected, the electric motor is
de-energized.
[0010] The motor protection device further includes an overload
detection unit. The overload detection unit is configured to
monitor a motor current and to control the interrupter unit to
switch from the operation mode into the overload mode if the motor
current indicates an overload condition of the electric motor in
the operation mode. The motor protection device further includes a
recovery detection unit. The recovery detection unit is configured
to monitor a motor temperature and to control the interrupter unit
to switch from the overload mode back into the operation mode if
the motor temperature indicates a recovery from the overload
condition.
[0011] In a further aspect, the overall objective is achieved by an
electric drive. The electric drive includes a motor protection
device according to any embodiment as disclosed above and/or
further below. The electric drive further includes an electric
motor. Optionally, the electric drive may include further
components such as a reduction gear and/or end switches. In some
embodiments, the electric drive is a servo drive or a spring return
drive.
[0012] In a further aspect, the overall objective is achieved by a
method for operating an electric motor. The method includes the
step of connecting the electric motor and a power supply in an
operation mode. The method further includes, in the operation mode,
monitoring a motor current and switching from the operation mode
into an alternative overload mode if the motor current indicates an
overload condition of the electric motor. The electric motor and
the power supply are disconnected in the overload mode. The method
includes monitoring, in the overload mode, a motor temperature of
the electric motor and switching from the overload mode back into
the operation mode if the motor temperature indicates a recovery
from the overload condition.
[0013] In a further aspect, the overall objective is achieved by
the use of a motor protection device according to any embodiment as
disclosed above and/or further below for operating an electric
motor.
[0014] A motor protection in accordance with the present invention
combines desired characteristics and advantages of different
approaches in a favorable manner, while avoiding or minimizing
their disadvantages. In particular, the detection of an overload
condition via the motor current has a minimal response time and
allows a quick disconnection of the motor from the power supply.
Further, the motor current indicates both an overload condition
while the motor is still running and a condition where the motor is
mechanically blocked. The temperature as measure for the recovery
from an overload condition provides a reliable criterion when the
motor can again be energized and connected with the power supply,
taking into account the overall application situation, in
particular the environmental temperature at which the motor is
operated. Thereby, it can be ensured that the motor is given
sufficient time for recovery and is not energized again too early,
while avoiding an unnecessarily long waiting time.
[0015] The above-mentioned advantages are associated with the fact
that the motor current reflects a change of the motor load
virtually immediately, while the motor temperature reacts slower
with a comparatively long time constant.
[0016] The switching from the overload mode into the operation mode
under control of the recovery detection unit may in particular
follow respectively be subsequent to a switching from the operation
mode into the overload mode under control of the overload detection
unit. Switching from the operation mode into the overload mode
occurs if the motor current indicates an overload condition, and
subsequent switching back from the overload mode into the operation
mode occurs if the motor temperature indicates a recovery.
Switching into the overload mode is accordingly current-based and
switching back into the operation mode is temperature-based.
[0017] In some embodiments, switching from the operation mode into
the overload mode is necessarily current-based and only occurs if
the motor current indicates an overload condition as explained
before. Additionally, or alternatively, switching from the overload
mode back into the operation mode is necessarily temperature-based
and only occurs if the motor temperature indicates a recovery. In
further embodiments, however, switching from the operation mode
into the overload mode and/or switching from the overload mode back
into the operation mode may optionally also be triggered by further
means. In particular, the overload detection unit may be configured
to monitor the motor temperature and to control the interrupter
unit to switch from the operation mode into the overload mode if
the motor temperature indicates an overload condition of the
electric motor in the operation mode.
[0018] The motor protection device may be realized as a
specifically designed circuit, using active components such as
integrated and/or discrete semiconductors components and passive
components as generally known in the art. However, the motor
protection device may also be realized fully or partly by one or
more programmable components, such as ASICSs, microprocessors or
microcontrollers with corresponding code respective programming.
This particularly holds true for the overload detection unit and
the recovery detection unit.
[0019] The motor protection device may include a power supply
interface and a motor interface that are designed for connecting
with the power supply and the electric motor, respectively. The
power supply interface and the motor interface may be realized as
releasable connectors such as plugs and/or sockets, but may also be
designed for example as soldering interfaces or, screw interfaces,
or the like. It is to be understood that the motor protection
device may be realized as dedicated and self-contained assembly,
and/or may be realized integral with further units or assemblies,
such as the power supply and and/or a power module. It is noticed
that a connection of the motor protection device with a power
supply and the electric motor may be direct or indirect, that is,
via further units, components, circuits or assemblies.
[0020] The electric motor may, in some designs, be an ordinary DC
motor or AC motor. In some favorable and typical embodiments,
however, the motor is an electronically commutated (EC) motor
respectively brushless DC motor. In such embodiment, a power module
may be foreseen to generate the drive signals for the one or more
motor coil(s), for motor speed regulation, and the like.
[0021] The power supply is in the following assumed as DC power
supply, such as a battery and/or electronic power supply unit that
provides a DC supply voltage. The power supply may, in other
embodiments, also be an AC power supply, in dependence of the
electric motor and the overall design.
[0022] The interrupter unit may include one or more switching
elements that are, in an operational configuration, electrically
arranged in series with the power supply and the electric motor.
The interrupter unit may include one or more electromechanically
switches, such as relays. In typical embodiments that are assumed
in the following, however, the interrupter unit is realized on
solid-state basis and includes one or more semiconductor
components, such as FETs or MOSFETs as voltage-controlled switches.
In further embodiment, the interrupter unit is formed integrally
with a power circuit, with one or more switching elements of the
power circuit, e. g. FET(s) or MOSFET(s), acting as interrupter
unit.
[0023] As will explained further below in more detail, the motor
protection device may include a bi-stable circuit that controls the
interrupter unit. The two alternative states correspond to the
operation mode and overload mode, respectively. Switching of the
bi-stable circuit and accordingly between the operation mode and
the overload mode is favorably controlled by control signals that
are generated by the overload detection unit and/or the recovery
detection unit.
[0024] In some embodiments, the motor temperature is a temperature
of one or more motor coils of the electric motor. Further in some
embodiments, the recovery detection unit is configured to monitor a
resistance of one or more motor coil(s). Corresponding methods for
operating an electric motor may include monitoring a resistance of
one or more motor coil(s). The recovery detection unit of such
embodiments includes a resistance monitoring circuit. The
resistance of the one or more motor coil(s) serves as indirect
measure respectively indicator for the motor temperature. In the
context of the present disclosure the term "resistance" is to be
understood as electrical resistance.
[0025] Monitoring a motor coil resistance as indirect temperature
indicator has the particular advantage that no additional sensors
and further no additional wiring for such sensors are needed.
Instead, the positive temperature coefficient (PTC) property of the
coil material, particularly copper, is exploited. As the
temperature of the motor coil(s) decreases, the resistance
accordingly also decreases.
[0026] In designs where the electric motor is an electronically
commutated motor, two or more, typically three single motor phases
are present, each phase embodying one or more coils and each phase
corresponding to one electrical contact of the motor. In
embodiments where the motor coils are configured as star (Y
configuration), the resistance that can be measured between each
two of the phases respectively contacts is given by the resistance
of the motor coils of two of the phases in series. In embodiments
where the motor coils are arranged as delta (A configuration), the
resistance that can be measured between each two of the phases
respectively motor contacts is the resistance of the motor coils of
one of the phases. A monitoring of the electrical resistance of one
or more motor coil(s) may in particular be a monitoring of a
resistance between two phases of the motor.
[0027] In alternative embodiments, the recovery detection unit is
configured to monitor the motor temperature by monitoring a
temperature in, at, or close to the motor, in particular the motor
coil(s), via a separate temperature sensing element. In such
embodiments, the recovery detection unit includes a temperature
monitoring circuit, with the temperature sensing element being part
of the temperature monitoring circuit.
[0028] In some embodiments, the motor protection device may be
configured to electrically connect a sensing input of the recovery
detection unit with the electric motor in the overload mode and to
disconnect the sensing input and the electric motor (M) in the
operation mode. This may in particular be the case in embodiments
where monitoring the motor temperature in the overload mode is
performed by monitoring the resistance of one or more motor coil(s)
as explained before and the sensing input is a resistance sensing
input. Here, the connection may be a connection with motor
contacts. The connecting and disconnecting may be achieved via one
or more switching elements, such as voltage-controlled switches.
The disconnection in the operation mode is favorable since
resistance monitoring would otherwise interfere with the regular
motor operation.
[0029] Further in some embodiments, the motor protection device may
be configured to provide power to at least part of the recovery
detection unit in the overload mode but not the operation mode. In
particular, resistors or voltage dividers of the recovery detection
unit may not be powered in the operation mode. This type of
embodiment has the advantage of reducing the overall power
consumption since the recovery detection unit is only powered when
needed.
[0030] In some embodiments, the motor protection device includes a
shunt resistor and the overload detection unit is configured to
monitor the motor current by measuring a voltage drop over the
shunt resistor. In such embodiments, the overload detection unit
includes a current monitoring circuit.
[0031] In some embodiments, monitoring the motor current includes
comparing the motor current with a given motor current threshold.
The overload detection unit may accordingly be configured to
compare the motor current with the motor current threshold. Further
in some embodiments, the motor current indicates an overload
condition only if the motor current exceeds the motor current
threshold for a given overload time threshold. The motor current
threshold defines an upper current limit that shall not be exceeded
in operation. The motor current indicating an overload
condition--and accordingly switching from the operation mode into
the overload mode--only if the threshold current is exceeded for a
given overload time threshold avoids a switching into the overload
mode in case of current peaks or temporary short overload episodes
that are considered as uncritical.
[0032] For comparing the motor current with a given motor current
threshold, the overload detection unit may include a comparator
circuit. The comparator circuit favorably compares a signal that
reflects the motor current, e. g. the voltage drop over a shunt
resistor as explained before, with a reference, for example an
overload reference voltage, reflecting the motor current threshold,
and provides an output depending on the results of the
comparison.
[0033] For determining if the motor current exceeds the motor
current threshold for a given overload time threshold, the overload
detection unit may include a timer, for example a countdown timer.
The countdown timer is started with an initial time value that
corresponds to the overload time threshold. The countdown timer is
stopped if the motor current falls below the overload current
threshold while running; in this case, the timer may then be reset
to the initial value or left at its position waiting for another
event where the motor current reaches a value higher than the motor
current threshold. Upon reaching zero, an output of the countdown
timer controls the switching from the operation mode into the
overload mode and the timer is reset to the initial value. In
alternative embodiments, alternative arrangements such as an
upwards-counting timer or a low-pass filtering of the motor current
signal may be used.
[0034] In some embodiments, monitoring the motor temperature
includes comparing the motor temperature with a given motor
temperature threshold. The recovery detection unit may accordingly
be configured to compare the motor temperature with the motor
temperature threshold. Further, in some embodiments, the motor
temperature indicates a recovery from the overload condition only
if the motor temperature remains below the motor temperature
threshold for a given recovery time threshold.
[0035] The motor temperature threshold defines a temperature limit
above which the electric motor shall not be energized again after
an overload, respectively, below which the motor temperature shall
be fallen before energizing the motor again. The temperature
indicating a recovery--and accordingly allowing switching back from
the overload mode into the operation mode--only if the motor
temperature is below the motor temperature threshold for a given
recovery time threshold is an additional safety measure that
prevents the motor from being energized again before it has
sufficiently recovered in case of short drops below the threshold
motor temperature.
[0036] For comparing the motor temperature with a given motor
temperature threshold, the recovery detection unit may include a
comparator circuit. The comparator circuit favorably compares a
signal that reflects the motor temperature, e. g. resistance
between two of the motor phases, respectively, a voltage drop over
the motor coil(s), with a reference, for example a recovery
reference voltage, that reflects the motor temperature threshold,
and provides an output in dependence of the comparison result.
[0037] For determining if the motor temperature is below the motor
temperature threshold for a given recovery time threshold, the
recovery detection unit may include a timer, for example a
countdown timer. The countdown timer is started with an initial
time value that corresponds to the recovery time threshold. The
countdown timer is stopped if the temperature rises above the
threshold motor temperature while running; in this case, the timer
may then be reset to the initial value or left at its position
waiting for another event where the motor temperature reaches a
value lower than the motor temperature threshold. Upon reaching
zero, an output of the countdown timer controls the switching from
the overload mode into operation mode and the timer is reset to the
original value. In alternative embodiments, alternative
arrangements such as an upwards-counting timer or a low-pass
filtering of the temperature signal may be used.
[0038] In some embodiments, at least one of the interrupter unit,
the overload detection unit and the recovery detection unit is
designed in an at least partly redundant manner. Exemplary designs
for this type of embodiment are explained in more detail further
below.
[0039] In some embodiments, the electric drive includes a power
module. The power module is electrically connected with the
electric motor. The interrupter unit is further electrically
connected or integral with the power module. The electric motor is
electrically connected with an output side of the power module. An
input side of the power module may be arranged in series with the
interrupter unit. In such embodiment, the input side of the power
module is, in an operational configuration, electrically connected
with the power supply in the operation mode, such that electric
power is supplied from the power supply to the electric motor. The
input side of the power module is electrically disconnected from
the power supply in the overload mode, such that no electric power
is supplied to the electric motor. In embodiments where the
electric motor is an electronically commutated motor, the power
module may include the circuitry for the commutation and
accordingly be designed to provide the drive signals for each of
the motor coils in a generally known manner. In some embodiments
with a power module, the interrupter unit is integral with the
power module. In such embodiments, switching elements of the power
module, such as MOSFETs or other semiconductor-based switching
elements, serve at the same time as interrupter unit. The input
side of the power supply may, in typical designs that are assumed
here, be suitable and/or designed for connecting with a DC power
supply and have a supply voltage terminal and a ground
terminal.
[0040] In some embodiments, the electric drive includes a reduction
gear coupled to the motor shaft of the electric motor. Further in
some embodiments, the electric drive is a spring return drive and
includes a return spring operatively coupled to the motor shaft
and/or a reduction gear. The electric drive may particularly be
designed as safety drive. Further, the electric drive may be
designed to be operatively coupled and controlled by an external
control device, such as an HVAC (Heating, Ventilation and Air
Conditioning) control and/or a fire protection system. It is noted,
however that a motor protection device and method are not limited
to a particular type of electric drive but may be used for all
kinds of electric drives with an electric motor that requires
overload protection.
[0041] The electric drive may be designed for operative coupling
with a driven element, in particular a valve or a damper, such as a
fire damper or smoke damper.
[0042] In case of the electric drive being a spring return drive,
the motor is energized during regular operation to maintain a
desired position of an output element of the safety drive, e.g., an
output shaft of the safety drive, in a desired position. Thereby,
the driven device 1s held in a desired operation position, for
example a fully opened position, a fully closed position, or any
desired intermediate position. In the non-energized state of the
motor, e. g. in an emergency situation or in case of a motor
overload, the return spring moves the output element of the safety
drive and accordingly the driven device into a pre-determined
safety position.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1 shows an embodiment of a motor protection device in
the operation mode;
[0044] FIG. 2 shows the embodiment of FIG. 1 in the overload
mode;
[0045] FIG. 3 shows a further embodiment of a motor protection
device in the operation state;
[0046] FIG. 4 shows the embodiment of FIG. 3 in the overload
mode;
[0047] FIG. 5 shows a still further embodiment of a motor
protection device;
[0048] FIG. 6 shows an electric drive in operative coupling with a
driven device.
DESCRIPTION OF THE EMBODIMENTS
[0049] In the following, reference is first made to FIG. 1 and FIG.
2. FIG. 1 and FIG. 2 show a first embodiment of a motor protection
device 1 in an operational configuration together with a power
supply, a power module 2 and an electric motor M as schematic
circuit diagram. FIG. 1 shows the operation mode and FIG. 2 shows
the overload mode. The electric motor M, the power module 2 and the
overload detection circuit 12 form, in combination, an electric
drive that is powered via the power supply.
[0050] The power supply is exemplarily assumed as constant voltage
DC power supply with supply voltage Vcc. It is noted that
throughout this document a voltage is generally assumed as measured
against ground (GND) potential.
[0051] The motor M is exemplarily assumed as electronically
commutated motor. The drive circuit 2 is designed as generally
known in the art. It generates at its output side the drive signals
for the three motor phases respectively the three motor coils (not
individually shown) of electric motor M from the supply voltage Vcc
which is supplied to the input side of the power module 2. The
input side of the drive circuit 2 is in this example given by a
supply voltage terminal and a ground (GND) terminal. The motor
coils may be configured as star respectively Y circuit, or as delta
(.DELTA.) circuit.
[0052] The motor protection device 1 comprises an interrupter unit
11, an overload detection unit 12, a recovery detection unit 13 and
a bi-stable circuit 14. The interrupter unit 11 is schematically
represented by a voltage-controlled switch with a control voltage
VoB. The control voltage VoB is provided by the bi-stable circuit
14 as explained further below. The input side of the power module 2
is coupled with the power supply respectively supply voltage Vcc
via the shunt resistor Rshunt if the voltage-controlled switch 11
is closed and disconnected from the power supply respectively
supply voltage Vcc if the voltage-controlled switch 11 is open.
[0053] The overload detection unit includes a comparator 121, a
timer circuit 122 and an overload voltage reference of overload
reference voltage Vref. For exemplary purposes, the comparator 121
is shown as being realized by an operational amplifier (OpAmp)
without feedback, as generally known in the art. Throughout this
document, OpAmps are generally assumed as ideal. The comparator
121, the shunt resistor Rshunt and the overload voltage reference
Vref form, in combination, a current monitoring circuit.
[0054] In the operation mode, a positive input of the comparator
121 is held on a constant voltage that is below the supply voltage
Vcc by the overload reference voltage Vref. While the overload
voltage reference is exemplarily shown as battery, it is in
practice typically realized by a Zener-diode or other kind of
voltage reference circuit as known in the art. The negative input
of the comparator 121 is connected with the supply voltage terminal
of the power module 2.
[0055] In the operation mode as illustrated in FIG. 1, the voltage
drop over the shunt resistor Rshunt that results from the current
drawn by the power module 2 and the motor M is smaller than the
overload reference voltage Vref. Consequently, the voltage at the
negative input of the comparator 121 is higher than at the positive
input, and the output of the comparator 121 will be LOW. (The
expressions LOW and HIGH are used in the ordinary sense of digital
respectively binary circuitry. LOW corresponds typically to ground
(GND) potential, while HIGH corresponds to a different
potential).
[0056] An overload condition occurs if the current that is drawn by
the power module 2 and the motor M reaches a value where the
voltage drop over the shunt resistor Rshunt exceeds the overload
reference voltage Vref. At this point, the voltage at the negative
input of the comparator 121 will fall below the voltage at the
positive input and the output of the comparator respectively OpAmp
121 will change from LOW to HIGH. This change at the output of
comparator 121 triggers a start of the optional timer circuit 122
that is connected with the output of comparator 121. An output of
the timer circuit changes its state (e. g. from LOW to HIGH or vice
versa) if the output of comparator 121 continuously stays HIGH for
a given overload time threshold. The overload time threshold may,
for example, be in a range of few seconds to several minutes. If
the output of the comparator 121 falls again to LOW potential
during this time interval, the output of the timer circuit 122 does
not change. The output of the timer circuit 122 is connected with a
first input, in particular a set input, of bi-stable circuit 14 and
is a first control signal. The bi-stable circuit may, for example,
be realized by a set/reset (R/S) flip-flop. As the output of timer
circuit 122 and accordingly the set input of the bi-stable circuit
122 changes its state as explained before, an output of the
bi-stable circuit 14 switches the control voltage Vob, thereby
controlling the interrupter unit respectively voltage-controlled
switch 11 to disconnect the power module 2 from the supply voltage
Vcc, such that the electric motor M is not further energized. The
motor protection device 1 accordingly switches from the operation
mode into the overload mode. In dependence of the implementation,
switching from the operation mode into the overload mode is
determined by a switching of the control voltage Vob HIGH to LOW or
vice versa.
[0057] The operation of motor protection device 1 in the overload
mode and the operation of recovery detection unit 13 is described
in the following with particular reference to FIG. 2.
[0058] The recovery detection unit 13 includes in this design a
comparator respectively OpAmp 131, similar to comparator 121, a
voltage divider with resistors Rcold, R1, a resistor R2 and
voltage-controlled switches 132, 133, 134. The voltage-controlled
switches 132, 133, 134 are also controlled by the control voltage
Vob, but operate complementary to the interrupter unit respectively
voltage-controlled switch 11 as explained before. That is, if the
voltage-controlled switch 11 is closed, the voltage controlled
switches 132, 133 134 of the recovery detection unit 13 are open,
and vice versa. Consequently, the voltage-controlled switches 132,
133, 134 are open in FIG. 1 (operation mode) and are closed in FIG.
2 (overload mode).
[0059] In the overload mode, a recovery reference voltage is
provided to the positive input of comparator 131. The recovery
reference voltage is tapped at the center tap between the resistors
Rcold and R1, which are arranged in series between the supply
voltage VCC and GND. The resistor Rcold is connected with the
supply voltage Vcc via the voltage-controlled switch 132, such that
the voltage divider that is formed by Rcold and R1 is powered and
operative only in the overload mode. It is noted that the recovery
reference voltage at the positive input of comparator 131 may
alternatively be implemented differently.
[0060] Further in the overload mode, one of the motor contacts of
Motor M (exemplarily motor contact A) is connected with the supply
voltage Vcc via the voltage-controlled switches 132 and 133.
Another motor contact (exemplarily motor contact C) is in the
overload mode connected via voltage-controlled switch 134 with
ground via the resistor R2 and further with the negative input of
comparator 131. The total resistance between motor contacts A and C
corresponds to the resistance of one or more of the motor coils, in
dependence of the configuration of motor M (delta (.DELTA.)
configuration respectively Y-configuration). The comparator 131,
the voltage divider with resistors Rcold, R1 and the resistor R2
form, in combination, an electrical resistance monitoring circuit.
The connection of voltage controlled switches 133, 134 to motor
contacts A, C form a resistance sensing input for the resistance
monitoring circuit 13.
[0061] While another dimensioning may be used as well, the
resistors R1 and R2 are dimensioned equally in this example. As
long as the resistance between the motor contacts A, C is higher
than the resistance of Rcold (corresponding to the motor
temperature being above the motor temperature threshold), the
voltage at the negative input of comparator 131 is lower than the
voltage at its positive input and the output of comparator 131 will
accordingly be HIGH. As a sinking motor temperature results in the
resistance between motor contacts A and C decreasing below the
resistance of Rcold (corresponding to the motor temperature being
below the motor temperature threshold), the voltage at the negative
input of comparator 131 will be higher the voltage at the positive
input. The voltage at the output of comparator 131 accordingly
changes from HIGH to LOW. The output of the comparator 131 provides
a second control signal and is connected with a second input, in
particular a reset input, of bi-stable circuit 14. Consequently,
the bi-stable circuit 14 will again switch the control voltage VoB,
such that voltage-controlled switches 132, 133, 134 are opened and
the interrupter unit respectively voltage-controlled switch 11 is
closed. The motor protection device 1 accordingly returns from the
configuration of FIG. 2 (overload mode) to the configuration of
FIG. 1 (operation mode).
[0062] It is noted that the resistors Rcold, R1, R2 are dimensioned
such that the current that flows through the motor M is favorably a
small monitoring current in order to avoid further heating of the
motor M. Since the current is a simple DC current without
commutation, the motor M will in any case not start.
[0063] In the following, reference is additionally made to FIG. 3
and FIG. 4, showing an embodiment of a power module similar to the
embodiment of FIG. 1 and FIG. 2 as explained before, with FIG. 3
showing the operation mode (similar to FIG. 1) and FIG. 4 showing
the overload mode (similar to FIG. 2). The following description is
focused on the differences.
[0064] In the embodiment of FIG. 3 and FIG. 4, the interrupter unit
respectively voltages controlled switch 11 and the shunt resistor
Rshunt are arranged at the input side of power module (2) in the
connection from power module 2 to GND. Further, the overload
voltage reference Vref is arranged to hold the negative input of
comparator 121 on a constant voltage that is above GND by the
overload reference voltage Vref. The positive input of comparator
121 is connected with the input side of the power module 2 via the
interrupter unit respectively voltage-controlled switch 11. As long
as the voltage drop over the shunt resistor Rshunt is smaller than
the overload reference voltage Vref, the voltage at the positive
input of comparator 121 will be below the voltage at the negative
input and the output of comparator 121 will accordingly be LOW. As
the voltage drop over the shunt resistor Rshunt exceeds the
overload reference voltage Vref, the voltage at the positive input
of the comparator 121 is higher than the voltage at the negative
input, and the output of the comparator 121 will accordingly change
from LOW to HIGH.
[0065] In the following, reference is additionally made to FIG. 5,
showing a further embodiment of a motor protection device. This
embodiment is similar to the embodiment of FIGS. 1, 2 and the
following description is focused on the differences. Further, the
individual units of the motor protection device 1 are not
referenced as such for the sake of clarity.
[0066] In the embodiment of FIG. 5, all voltage-controlled switches
are specifically shown as MOSFETs. A major difference to the
embodiment of FIG. 1 and FIG. 2 is that the interrupter unit and
the bi-stable circuit are designed in a redundant manner. Further,
the overload detection unit and the recovery detection unit are
designed in a partly redundant manner.
[0067] The interrupter unit comprises two MOSFETs Q1, Q2 in serial
arrangement. MOSFET Q1 is controlled by a first control voltage
VoB1 and MOSFET Q2 is separately controlled by a second control
voltage VoB2. An electrical connection of the input side
respectively the supply voltage terminal of the power module 2 with
the supply voltage Vcc requires both MOSFETs Q1, Q2 to be
switched-on respectively connected through. The first control
voltage VoB1 is provided by a first bi-stable circuit 14-1 and the
second control voltage VoB2 is provided by a separate second
bi-stable circuit 14-2. Similarly, first and second overload
reference voltages Vref1, Vref2, first and second comparators
121-1, 121-2, and first and second timer circuits 122-1, 122-2 are
provided. The negative inputs of the comparators 121-1, 121-2 are
connected with the supply voltage terminal of the power module 2.
The coupling is in this example via coupling resistors Rin1, Rin2.
The resistors Rin1, Rin2, Rin3, Rin4, Rin5, Rin6 connected to the
inputs of the comparators 121-1, 121-2, 131-1, 131-2 are introduced
in order to avoid that a fault in one comparator will influence the
redundant comparator (e.g. comparators 121-1 and 121-2). This is
beneficial in applications where the motor protection 1 unit is
required to achieve a first-fault robustness.
[0068] In the shown design, the first comparator 121-1 and the
second comparator 121-2 separately compare the voltage drop over
the shunt resistor Rshunt with the (substantially identical)
overload reference voltages Vref1 and Vref2, respectively. The
outputs of the comparators 121-1, 121-2 separately connected with a
first input, in particular a set input, of associated bi-stable
circuit 14-1 respectively 14-2 via a timer circuit 122-1
respectively 122-2 as explained before.
[0069] The recovery detection unit includes separate comparators
131-1, 131-2, the output of which are each connected with the
second input, in particular a reset input, of the associated
bi-stable circuit 14-1, 14-2. The voltage divider with resistors
Rcold, R1 operates in substantially the same way as explained
before. In contrast to the embodiment of FIGS. 1, 2, however, two
voltage-controlled switches in form of MOSFETs Q3, Q4 are arranged
between R1 and ground. The positive inputs of the comparators
131-1, 132 are each separately connected with the center tap
between Rcold and R1 via (identical) separate coupling resistors
Rin3, Rin5. For coupling the motor terminals, A, C with the supply
voltage Vcc and the resistor R2, two pairs of voltage-controlled
switches in form of MOSFETs are provided, with MOSFETs Q5, Q6 being
arranged in series between motor contact C and, Vcc while MOSFETs
Q7, Q8 are arranged in series between motor contact A and R2. In
each pair Q5, Q6 respectively Q7, Q8, one of the MOSFETs is
controlled by the first control voltage VoB1, while the other
MOSFET is controlled by the second control voltage VoB2. The
resistor R2 is connected with the negative input of both
comparators 131-1, 131-2 via coupling resistors Rin4, Rin6. All
coupling resistors Rin1 . . . Rin6 may be dimensioned identically.
It can be seen that the MOSFETs Q3 and Q4, Q5 and Q6, Q7 and Q8 are
arranged pairwise in series. In this way single fault robustness is
achieved in that each MOSFET of a pair can interrupt the circuit
even if the other MOSFET of the pair is shortcut.
[0070] In the described embodiments, no recovery time threshold is
taken into account as explained in the general description. If a
recovery time threshold shall be taken into account, one or more
timer circuit(s), similar to timer circuits 122, 122-1, 122-2 may
for example be introduced between the output of comparators 131,
131-1, 131-2, and the bistable circuits 14, 14-1, 14-2.
[0071] In the following, reference is additionally made to FIG. 6.
FIG. 6 schematically shows an electric drive 99 in operative
coupling with a driven device 5. The driven device 5 may for
example be a valve or a damper. The electric drive 99 includes a
motor protection device 1, a power module 2 and an electric motor M
as described before. The electric motor M is coupled with the
driven device 5 via an optional reduction gear 3. In the shown
embodiment, the electric drive is exemplarily realized as spring
return drive with an optional return spring 4. The return spring 4
is operatively coupled to the force/torque flow between the motor M
and the driven device 3.
[0072] Optionally, an external control device 6, such as a HVAC
control and/or fire protection system is operatively coupled with
the electric drive 99 for controlling the electric drive 99 during
regular operation as generally known in the art.
REFERENCE SIGNS
[0073] 1 motor protection device [0074] 2 power module [0075] 3
reduction gear [0076] 4 return spring [0077] 5 driven device [0078]
6 external control device [0079] 11 interrupter
unit/voltage-controlled switch, MOSFET [0080] 12 overload detection
unit [0081] 121, 121-1, 122-2 comparator/OpAmp [0082] 122, 122-1,
122-2 timer circuit [0083] 13 recovery detection unit [0084] 131,
131-1, 131-2 comparator/OpAmp [0085] 132, 133, 134 voltage
controlled switch, MOSFET [0086] 14, 14-1, 14-2 bi-stable circuit
[0087] 99 electric drive [0088] M electric motor [0089] Rcold, R1,
R2, Rin1, Rin2, Rin3, Rin4, Rin5, Rin6 resistor [0090] Rshunt shunt
resistor [0091] Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 MOSFET [0092] Vref,
Vref1, Vref2 overload reference voltage [0093] VoB control voltage
[0094] VoB1 first control voltage (in case of redundancy) [0095]
VoB2 second control voltage (in case of redundancy) [0096] A, B, C
motor contact [0097] Vcc supply voltage [0098] GND ground
* * * * *